Since 8.0 Oreo, Android has had what's called notification channels, a way to filter notifications from apps based on the type of activity each notification is alerting you to. Not all apps support the feature, though. Until recently, Facebook — which notifies you when you get a comment, when you're tagged in something, when it's someone's birthday, et cetera — was one such app. Now, though, you can choose only to receive the notifications you care about.
Last weekend, reports on Reddit said that the app gained notification channel support with version 18.104.22.168.72, but others on the same version said they weren't seeing it yet; your mileage may vary. We were only recently able to get it working by clearing data in the Facebook app then tapping the Device-Level Notifications option in its notification settings.
You can fiddle with these settings for yourself in Settings > Apps & notifications > Facebook > Notifications. Outside of the option to turn notifications on or off altogether, there are 17 categories of notification you toggle. Finally, no more alerts for people you may know.